The present invention relates generally to metallic connectors, that is, devices that join together multiple parts by means of an intervening member, particularly connectors having one or more elements made of material that possesses super-elastic properties. The present connectors are suitable for high-performance industrial and medical applications involving different ranges of operating temperatures and component materials being connected.
The present inventor has previously filed application Ser. No. 09/311,938 entitled xe2x80x9cStress Induced Sealxe2x80x9d on May 14, 1999, Ser. No. 09/440,064 entitled xe2x80x9cStress Induced Gasketxe2x80x9d on Nov. 15, 1999 and Ser. No. 09/501,109 entitled xe2x80x9cStress Induced fastenerxe2x80x9d on Feb. 9, 2000, the entire disclosures of which are expressly incorporated by reference herein and relied upon.
The use of metallic super-elastic alloys, such as Nixe2x80x94Ti (nitinol) and other bi- or tri-metal alloys, has been documented in a variety of technical applications, including fasteners, connectors, gaskets, clamps and seals. Many such uses have required temperature in order to activate the material and change its physical state, while others have used mechanical forces that impart stress to cause a super-elastic physical deformation in the material. Of particular concern to the instant inventor is the application of the super-elastic material to connectors. The use of non-corrosive, metallic super-elastic material offers a decided advantage in high performance connecting assemblies, versus more conventional connectors requiring threaded fasteners, springs, clamps or other holding or securing mechanisms. Particularly it can withstand more wear than alloys used in conventional connectors due to its harder surface characteristics. It can also withstand extreme vibrations and not loosen due its elastic preloaded condition without using conventional adhesives to hold the assembled components and/or the connector itself together. Adhesives used with conventional connectors make them very difficult to disassemble, whereas it is generally possible to make a super-elastic connector completely reversible.
U.S. Pat. Nos. 5,395,193 and 5,584,631 to Krumme et al., discuss the use of nickel-titanium shape memory retainers in an optimized elastic condition that have super-elastic or pseudo-elastic properties. These fasteners are said to be useful for eyeglass assembly; they are placed onto a pin to retain components together. However, this use does not contemplate an interposed connector.
U S. Pat. No. 5,683,404 to Johnson, entitled xe2x80x9cClamp and Methodfor its Usexe2x80x9d, further discusses shape memory materials that are xe2x80x9cpseudo-elasticxe2x80x9d, defining these materials in terms of their ability to exhibit super-elastic/pseudo-elastic recovery characteristics at room temperature. Such materials are said to deform from an austenitic crystal structure to a stress-induced structure postulated to be martensitic in nature, returning thence to the austenitic state when the stress is removed. The alternate crystal structures described give the alloy super-elastic or pseudo-elastic properties. Poisson""s Ratio for nitinol is about 0.3, but this ratio significantly increases up to approximately 0.5 or more when the shape memory alloy is stretched beyond its initial elastic limit. It is at this point that stress-induced martensite is said to occur, i.e., the point beyond which the material is permanently deformed and thus incapable of returning to its initial austenitic shape. A special tool is employed by Johnson to impart an external stretching force that deforms the material which force is then released to cause the material to return to its original condition. While the device is stretched, a member is captured by it and securely clamped when the stretching force is released. This device is intended for use in clamping and does not contemplate traditional connecting operations of the kind addressed by the present invention. Another use envisioned by Johnson is in connecting the modular components of a medical device, as described in his U.S. Pat. No. 5,858,020, by subjecting a thimble component made of shape memory material to an external stretching stimulus to elongate and thereby reduce its transverse dimension. Upon release of the stretching force, this component returns towards its original rest dimension, contacting and imparting a force on another component. This is a sequential stretching and relaxation of the super-elastic material rather than a simultaneous activation and retention operation. Also, special structures are necessary on the thimble to allow the stretching force to be imparted.
In U S. Pat. No. 5,197,720 to Renz, et al., a work piece is held within a clamping tool by an expansion element made of shape memory material that is activated by mechanical force. In this way, torque is transmitted through the shape memory member. This device is useful for bringing parts together for holding the work piece in order to perform an operation. It does not, however contemplate a use as a connector. U.S. Pat. No. 5,190,546 to Jervis discloses insertion into a broken bone cavity of a split member made of shape memory material using a super-elastic alloy. The split member holds the walls of the bone cavity when radial compressive forces acting on it are released. In order for the radial compressive force to reduce the diameter, the component must be split, allowing the reduction in dimension for insertion. It does not act as an interposed member in a connecting assembly.
Others have sought to utilize the properties of shape memory materials as locking, connector and bearing elements, e. g., U.S. Pat. Nos. 5,507,826 to Besselink, et al., 5,779,281 to Kapgam, et al., and 5,067,827 to, Arnold respectively; however, such approaches have required temperature to be applied during use. U.S. Pat. Nos. 5,277,435 to Kramer, et al. and 5,876,434 to Flomenblit, et al. similarly has relied upon temperature to activate the shape memory effect. Such dependence on extrinsic activation by temperature introduces an added process step and may further be disadvantageous in certain other applications.
U S. Pat. No. 5,842,312 to Krumme, et al., entitled, xe2x80x9cHysteretic Damping, Apparati and Methodsxe2x80x9d, employs shape memory tension elements to provide energy dissipation. Such elements can be placed between building structures, etc., which are subject to vibration, serving to absorb the energy created by their relative movement. However, this patent does not contemplate the vibration dampening effect of a super-elastic material in the formation of a connector.
Accordingly, there is a need to form a connecting assembly using a durable metallic, non-corrosive connector assembly, which are simple to install using relative motion to activate the assembly.
There is a further need to form a secure connection between components that minimizes the micro-motional wear characteristics of the assembly, enhancing its useful life.
There is another need to form a fastened assembly that does not require temperature for its activation.
There is still a need to form an assembly using a fastener that adjusts for differences in thermal coefficients of expansion or contraction of dissimilar materials comprising those components being fastened.
There is still a further need for a connector with elastic properties that allow more forgiving tolerances during manufacturing of the assembly components.
According to the present invention, a connecting assembly has at least two components. A first component defines a given shape with a cross section having a first dimension. A second component defines a second given shape having a cross section which is continuous with at least a second dimension sized with interference to the first dimension, the second component being made of a super-elastic alloy. One of the first and second components includes an opening that corresponds to its associated cross-section wherein relative motion causes the first dimension to contact the second dimension, imparting a force to super-elastically expand or contract the second dimension, allowing them to be jointly retained.
According to an embodiment of the present invention, a connecting assembly has a first component defining an opening, a second component adapted to be retained together with the first component and a connector component made of a superelastic alloy. Relative motion between at least two of the components causes a super-elastic activation of the connector wherein the activation simultaneously retains the components together with the connector interposed jointly therebetween.
In a preferred embodiment of the present invention, the connector component is pre-assembled to one of the first and second components. More preferably, the first component is pre-assembled with the connector the second component is moved relative to the pre-assembled components to activate the superelastic alloy of the connector. Alternatively, the second component is pre-assembled with the connector and the first component is moved relative to the pre-assembled components to activate the superelastic alloy of the connector.
In another preferred embodiment, the first and second components are pre-assembled and relative motion occurs between the connector and the pre-assembled components.
In yet another embodiment of the present invention, the opening defines an axis and relative motion occurs along the axis; alternatively, the relative motion could occur normal to the axis.
In still another embodiment of the present invention, the components are rigidly retained.
In still yet another embodiment of the present invention, the connection forms a seal.
An advantage of an embodiment of the present invention is that a super-elastic alloy, e. g., nickel-titanium has an oxide layer presenting a stronger wear surface than other traditional connectors. Moreover, the connector component is elastic in nature, allowing it to act as a vibration-dampening member that prevents the assembly from loosening. Also, the components of the present assembly are more forgiving of manufacturing tolerances. These connectors are entirely reversible.
Another advantage of an embodiment of the present invention is that a connection is effected by simple relative motion, not requiring threaded fasteners, springs, clamps or other holding or securing mechanisms. This feature allows the connectors to be operable in a much smaller working space, further avoiding the complexity associated with traditional connection devices.
A further advantage of an embodiment of the present invention is that the super-elastic properties are not dependent on temperature to impart the activaton force required to effect such a connection.
Other objects and advantages will be appreciated by those skilled in the art by resort to the appended Drawings having reference numerals that correspond to the ensuing Description of one or more embodiments of the invention wherein the following Figures are further elucidated.